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Washington (CNN) — Long before computers or televisions existed, a man who would become a U.S. senator and then president started an affair with his neighbor’s wife.

Even telephones were relatively new back then, so Warren Harding wrote Carrie Phillips smoldering love letters during their 15-year relationship that ended prior to his inauguration in 1921.

“I love you more than all the world, and have no hope of reward on Earth or hereafter, so precious as that in your dear arms, in your thrilling lips, in your matchless breasts, in your incomparable embrace,” said a 1910 letter first revealed in the book “The Harding Affair” by James David Robenalt.

Snail mail

Almost a century later, the snail mail between Harding and Phillips becomes fully public later this month, revealing the most intimate secrets and thoughts of a man destined for the pinnacle of power as America endured the First World War.

In his book, Robenalt examines the possible historical impacts of the affair, noting that Phillips may have spied for Germany and influenced Harding against running for president in 1916 as the war approached.

“There’s that sex steamy side to these letters,” he told CNN in an interview Monday. “But there’s also the big question of whether the United States should get involved in the First World War. They really debated that back and forth. She was really pro-German, he was very pro-American.”

Of equal interest, especially in the modern era of celebrity scandal mongering, is the pure salaciousness of the letters’ content.

“They really are very graphic love letters,” said Robenalt, who came across them while researching his 2009 book. “And people think that 100 years ago nobody had sex fantasies and I keep telling people if those people didn’t have sex fantasies, we wouldn’t be here today.”

Keeping such a secret seems impossible in today’s digitally monitored world. Not so back in 1905, a decade before the first coast-to-coast long distance phone call.

Salacious details

As outlined by Robenalt’s book, Harding was married at the time and serving as Ohio’s lieutenant governor.

He recommended that his friend and neighbor Jim Phillips, Carrie’s husband, go to a sanitarium that spring to help recover from the death of their 4-year-old son a year earlier. Meanwhile, Harding’s wife Florence was recovering from a kidney disease.

By August, Harding’s affair with Carrie commenced, though it only became physical three years later, according to Robenalt’s book.

“I do love you so,” he wrote in 1913, two years before his election as Republican senator from Ohio. ” I wonder if you realize how much—how faithfully, how gladly, how reverently, how wistfully, how whole-heartedly and how passionately. Yes, you do know the last, you must have felt the proof, but you can’t know the others.”

The same letter also showed Harding’s concern about the affair being discovered, long before the Internet age.

“I have been thinking of all those letters you have,” wrote, adding that “I think you have a fire, chuck ’em! Do. You must. If there is one impassioned one that appeals to you, keep it until you are tired of it, but chuck the rest. Why it frightens me to think I ever dared mail them to your address.”

By 1916, circumstances had changed, according to another letter.

From “enraptured bliss” to “depths of anxiety”

“It is a little more than thirty-six hours since I saw you, and they have all been given to you, amid the perturbation I could not shake off,” Harding wrote after what Robenalt said was a secret visit to Phillips in Marion, Ohio.

“If you designed to punish me you have succeeded fully,” the letter continued. “I came with heart a hungering, I knew the flight to enraptured bliss, and was then suddenly plunged to the depths of anxiety.”

The problem? Someone named Robinson, described by Robenalt as a rival lover, came to Marion.

“I had feared for a year, but would not surrender,” Harding’s letter continued. “I know now of my failure. I sought the impossible, and I am defeated.”

Robenalt noted the influence of the pending war at that time.

“He ultimately voted for war,” the author said of Harding. “He knew that it would probably ruin their relationship, and kill him politically in a state that had a lot of German-Americans.”

The affair ended four years later, as Harding ran for president in an election he won easily over Democrat James Cox. He didn’t survive his first term, dying of illness in 1923.

In a recent statement, the Library of Congress announced it would make the more than 1,000 pages of love letters public on July 29, with a discussion about them scheduled for July 22 in the Mumford Room of the James Madison Building in Washington.